Unable to find valid certification path

[megankatsumi]

I am using w3id.org a means of creating persistent, de-referenceable namespaces for a set of ontologies. Recently, I have encountered the following error when attempting to load the ontologies in Protege via the w3id url: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

This is the first time I've encountered such an issue, (and have not recently updated Protege); the ontologies have been loading successfully via the w3id url prior to this. They also still load successfully via their current url on GitHub.

Any suggestions to fix this?